This invention relates in general to vehicular braking systems, and in particular to a noise attenuator in a hydraulic control unit of an anti-lock vehicular braking system.
The use of attenuators which reduce amplitude of pressure fluctuations in hydraulic fluid lines of vehicular braking systems is well known. In particular, attenuators are common in vehicular anti-lock braking systems (ABS) at the outlet end of an ABS hydraulic pump used to generate supplemental brake fluid pressure. A hydraulic control unit (HCU) includes a housing having bores for mounting valves and the like and channels for directing fluid. An attenuator is mounted in a bore in the HCU to significantly reduce the amplitude of high energy pressure pulses in the brake fluid at the outlet of the pump. Such pressure pulses can be in the order of 900-1000 psi and can create noise which is transmitted to the master cylinder or its connection to the vehicle. An attenuator at the outlet end of the pump can reduce the pressure pulses to about 100-300 psi, thereby substantially reducing or eliminating noise associated with such pulses.
A conventional attenuator includes a closed chamber filled with brake fluid. An inlet passage delivers fluid from the outlet end of the pump. An orifice of substantially reduced diameter directs fluid from the chamber to an outlet passage. The restriction of fluid flow through the orifice attenuates pressure fluctuations as a result of the compressibility of the brake fluid. Thus, brake fluid in the chamber absorbs high energy fluid pulses and slowly releases the fluid through the orifice.